United went behind to an early Phil Jones own goal but battled back valiantly with goals from Dimitar Berbatov, spearheading the team in Wayne Rooney's absence, and Darren Fletcher. The Portuguese visitors responded swiftly through Pablo Aimar to keep their unbeaten run this season intact and a Nani cross that deflected behind in injury time proved the final throw of the dice.
As it stands, United are second in Group C - level on points with Benfica but crucially behind Tuesday's opponents on the head-to-head format - with Jorge Jesus' outfit due to play Otelul Galati in the final round. Basel held out for a 3-2 victory in Romania and they sit only a point behind last season's runners-up in the table.
The Reds got off to a nightmare start when an incisive move down the right in the third minute saw Maxi Pereira feed Nicolas Gaitan and the winger's cross was shinned into his own net by Jones, giving David De Gea no chance.
Gradually, Sir Alex's side responded, largely through Nani's adventurous dribbling, with Artur brought into action by the Portugal international's free-kick and a shot from Ashley Young. The visitors continued to try and disrupt the Reds' flow but the breakthrough came on the half-hour mark. Young worked a free-kick short to Patrice Evra who helped it on to Nani, always likely to be the source of any inspiration. The wide man's left-wing cross was perfect for Berbatov to guide a splendid header wide of Artur and into the net for the equaliser.